Among acceleration sensors manufactured based on MEMS technology, there have been manufactured some acceleration sensors equipped with electrostatic capacitors of which electrostatic capacity is changeable according to acceleration. For instance, a typical electrostatic capacitor for an acceleration sensor consists of a fixed electrode fixed to a substrate and a movable electrode installed on a weight which is movable with respect to the substrate so that the acceleration sensor employing such an electrostatic capacitor can detect acceleration associated with a change of electrostatic capacity in the electrostatic capacitor (for instance, Japanese Laid-Open Patent Publication No. 11-344507). The acceleration sensor disclosed in Japanese Laid-Open Patent Publication No. 11-344507 is configured such that, regarding a weight (mass body) having a rectangular shape long in the x-axis, its x-axis directional both ends are connected to a substrate via supports fixed to the substrate and elastic members (for instance, springs) while electrostatic capacitors are arranged separately at y-axis directional both sides of the weight to move in the x-axis direction. Thereby, the acceleration sensor disclosed in the Publication is provided as a uniaxial acceleration sensor in which a change of electrostatic capacity caused when the weight moves in a detection direction (x-axis direction) is outputted in proportion to acceleration speed.
Further, each movable electrode of the above acceleration sensor is arranged extending in one direction (y-axis direction) from the weight so as to face a fixed electrode installed on the substrate. Thus, the acceleration sensor disclosed in the above Publication is provided as a uniaxial acceleration sensor in which a change of electrostatic capacity is outputted based on a change of distance between the fixed electrode and the movable electrode that is caused when the weight moves in the detection direction (x-axis direction).
Besides the above-mentioned uniaxial acceleration sensor for detecting acceleration working in a single direction, there have been some three-dimensional acceleration sensors capable of detecting three dimensional acceleration, i.e., in x, y and z axis directions (for instance, Japanese Laid-Open Patent Publication No. 07-245413, Published Japanese Translation of PCT International Patent Application No. 2005-534016, Japanese Laid-Open Patent Publication No. 06-258340, Japanese Laid-Open Patent Publication No. 05-340960, Japanese Patent No. 2773495, Japanese Patent No, 3327595, etc.). For instance, an acceleration sensor disclosed in Japanese Laid-Open Patent Publication No. 07-245413 is configured such that a weight is connected to four beams each fixed to a substrate so as to allow the weight to move three dimensionally, i.e., with respect to x-axis, y-axis and z-axis axis directions. Regarding the acceleration sensor disclosed in the Publication, with reference to the center of the weight (the center when the weight is seen from the top), electrostatic capacitors are separately arranged for detecting acceleration working in the x-axis direction and acceleration working in the y-axis direction, wherein the x-y plane is parallel with a plane direction of the weight. Further, movable electrodes of the electrostatic capacitors are arranged extending in respective axial directions from the weight so as to face associated fixed electrodes.